The invention relates to a safety device for cutting off gas pipelines when temperature increases in an unacceptable way according to the preamble of the first patent claim.
Such thermal valve safety devices that are employed in pipelines, such as upstream from gas apparatuses, gas meters, etc., are available in a large variety of designs. They are used to interrupt gas supply before temperature increases at the aforementioned gas apparatuses to such level that their external tightness is jeopardised.
EP 118 152 A1 describes a valve in which a ball is kept respectively in open and, after reaching a limit temperature in closed position both by a spring and also by an alloy with thermal shape memory, with the spring being in such shape that automatic opening is impossible after closing.
The disadvantage of this solution is that the component of an alloy with thermal shape memory, located in the housing interior, has to be subjected to the higher temperature in order to achieve the desired closing of the valve. This means that the entire valve has to be heated in order to attain a response of the thermo-sensitive part by conduction of said heat. And it is necessary to place such valve immediately adjacent to each component that is jeopardised by temperature increase in order to detect the temperature in the area and, if need be, cut off the gas pipeline.
EP 343 615 A1 describes a valve with a cone as cut-off element. In this solution a guide rod is led through a valve cover and connects said plug with a fuse body that is pre-tensioned against the cover by means of a pressure spring. Softening of the fuse body removes the guide rod from the former so that, under the impact of the pressure spring, the plug can move abruptly in the closing direction.
Also this solution has the disadvantage that, on the one hand, the thermo-sensitive element is positioned in the housing interior and, hence, also the entire valve has to be heated and, on the other, such a valve has to be placed directly adjacent to each component that is jeopardised by temperature increase.
A thermal safety valve is also known from the utility model DE 94 20 607. This thermal safety valve is essentially of the same construction as the solution described above, i.e. the housing is provided with a soft solder which keeps a cut-off element, in this case a valve cone, in open position. Additionally a heating jacket, which is preferably electrically heatable, is provided at the valve housing in the area of the internal soft solder, so that the safety valve does not only actuate automatically after the soft solder is directly subjected to the higher temperature but which also facilitates its remote actuation.
The disadvantage of this solution is, that besides its complicated construction, it is necessary to provide additionally a source of auxiliary energy, piping and respective actuation elements.
EP 637 457 A1 describes an automatic closing device for a shut-off device. The element inhibiting the closing force has at least one pressure-actuated hollow body with a variable volume with a rated breaking point of a material whose melting temperature is adjusted to a defined limit value temperature. Upon achieving or exceeding said limit value temperature the closing operation is triggered by melting of the breaking point material and a subsequent pressure relief. The force of pressure in the hollow body is reduced and the closing force is activated. The rated breaking point can be executed as a reaction line that can be laid at any distance from the shut-off device so that a fire occurring in the reaction line yet at a distance from the shut-off device triggers the closing action.
The disadvantage of the latter solution is that the reaction line has to cover the entire area of the unit to be protected which, particularly in case of large units, entails disproportionately high costs.
DE 296 12 921 U1 describes a cut-off device for a gas pipeline system with a cut-off element that is kept in open position by at least one closing force-inhibiting element. The element has at least one pressure-actuated hollow body with a variable volume that is connected to a so-called function line consisting of a material whose melting temperature is adjusted to a defined limit value temperature. Melting of the function line causes a pressure drop in the hollow body and the closing force actuates the cut-off element so that the cut-off device is closed and the flow through the pipeline is discontinued. The pipeline outlet is additionally provided with a backflow check valve which, upon a pressure drop in the pipeline, prevents a gas backflow from the downstream pipeline.
In this cut-off device there is a pressure in the hollow body and the function line which is required to keep the cut-off element in the open position. Said pressure, however, is independent of the pressure in the gas pipeline.
It is also known that so-called gas flow control valves are used to automatically cut off gas pipelines. Said gas flow control valves are used to interrupt gas supply upon increase of gas consumption beyond a defined value.
The disadvantage of such gas flow control valves is that, in case of a damage at the gas pipeline, e.g. by a fire, and with a closed gas apparatus the gas volume flowing from the leak will have to be larger than the gas volume flow otherwise required for the operation of the gas apparatus before the gas flow control valve is closed.
The invention is focusing on the issue of developing a safety device for cutting off gas pipelines of the described type wherein the gas transfer through the safety device is prevented when temperature increases in the section of said safety device placed downstream from the gas pipeline, especially when connected gas apparatuses are in a closed position. In addition, it shall be possible to avoid an excessive pressure rise in the downstream pipeline. The aim of the invention is to maintain production costs and dimensions at a level as low as possible. According to the present invention the problem is solved by providing a safety device with a check valve that prevents a backflow from the gas pipeline which is placed downstream from said device and by arranging a pressure sensitive element which is actuated by the pressure in the pipeline downstream from said safety device. Said pressure sensitive element is coupled to a cut-off valve in such a way that when pressure increases in the downstream pipeline said valve prevents gas from flowing into the pipeline.
Thus a solution has been found that removes the disadvantages of the prior art that a thermal element in the housing interior has to be actuated by the higher temperature in order to achieve the desired closing of the valve. It is also no longer necessary to place such valve directly adjacent to each component that is jeopardised by a temperature increase in order to detect the temperature in this area and, if need be, cut off the gas pipeline. Further distinguishing features of this solution are above all its simplicity and production dimensions.
Further advantageous arrangements of the invention are described in the other patent claims. In order to prevent, for instance, the pressure rise from becoming excessively high after a temperature increase in the downstream pipeline a backflow can be released from the downstream pipeline by the check valve or a by-pass circumventing said check valve, after the gas transfer into the downstream pipeline has been cut off by the cut-off valve, with the cut-off valve also releasing backflow from the downstream pipeline.
In order to largely simplify assembly the movable cut-off element of the check valve can be a piston or a diaphragm which is loaded by a spring and/or its own weight against the gas flow direction. The piston or diaphragm disk can simultaneously form the pressure sensitive element.
A particularly advantageous form of execution in terms of manufacturing and cost-effectiveness is achieved when a rising pressure in the gas pipeline placed downstream from the safety device moves the piston into a bore and a return movement of the piston is prevented by the engagement of a latching stop. The bore is sealed by a flexible sealing at the piston.
In order to obtain a stroke motion of the piston by an initially low friction between piston and seat already at a low pressure and simultaneously ensure tightness at rising pressure the bore is preferably tapered in the moving direction of the piston.
Preferably, the section of the bore that is assigned to the piston after the engagement of the latching stop has an expansion. The fact that the diameter of said expansion is larger than the diameter of the piston with flexible sealing creates a gap between piston and expansion through which the pressure in the downstream pipeline is relieved. Following said pressure relief the piston, under the impact of a spring and/or its own weight as well as the latching stop, is again outside of the expansion and its flexible sealing seals the bore.
A particularly simple construction in terms of manufacturing is obtained when the latching stop comprises an expansion of the bore and a flexible sealing. In this case the diameter of the expansion is smaller than that of the piston with a flexible sealing. In addition, the expansion-to-bore transition has a limit stop.
A further form of execution of the inventive safety device for cutting off gas pipelines is attained by coupling the pressure sensitive element to an already known gas flow control valve in such a way that the gas flow control valve is in a closed position after a pressure rise in the downstream pipeline. This can be achieved, e.g., by the pressure sensitive element releasing the lock of a pre-tensioned spring when pressure increases and the gas flow control valve is moved into its closed position by the impact of the spring.
Said coupling with a gas flow control valve makes it possible to safely close the downstream pipeline in an emergency case, irrespective of the operating state of the connected gas apparatus.
The axial movement of the piston is preferably limited on either side by a seat with the seat upstream from the piston forming the check valve together with the piston, while the seat downstream from the piston forming the gas flow control valve together with the piston.
In order to avoid an abrupt movement of the piston from its operating position upon switching on the gas apparatus, and thus a premature response of the gas flow control valve, the piston has, at least at one front face, an extension which slides with loose fit in a guide aperture which is gas-tight closed at the front side. Thus, the opening process is damped.
Further advantageous executions are obtained when the safety device has a manipulator that can be externally actuated and is used to take the spring into the pre-tensioned and locked position or/and with which the safety device in a closed position can be brought into its initial position.
Its is also possible to arrange a number of safety devices in a gas distributor.